1. Field of the Invention
This invention relates to an image input method for inputting and displaying images of an object which makes periodical movements on a TV monitor screen and to a synchronous image input system for realizing the method.
2. Discussion of the Background
There are known various methods for imaging an object in order to detect a temperature thereof and for displaying temperature distribution thereof in thermal images. If the object is rotating, it is necessary to measure temperature on various locations of the object while it is rotating because if the movement is suspended, the temperature distribution might change.
As a prior art system for detecting infrared radiation from an object with raster scanning and imaging the temperature at various points, there is known an optical mechanical raster scanning system disclosed in U.S. Pat. No. 3,626,091 which can detect temperatures of a rotating object. FIG. 5 shows the principle of a camera head of the raster scanning system. The system shown in the figure is capable of obtaining one frame of image (one screen) in real time of 1/20 sec. by means of a polygonal rotary mirror 1 which is driven by a motor and which has ten faces and an infrared detector 2 having ten component elements. Each element of the infrared detector 2 detects one portion obtained by dividing an image vertically into ten. When the rotary mirror having ten faces rotates once, infrared images for one frame are scanned. More specifically, infrared video images 3 may be obtained simultaneously from each of the ten elements. Each of the ten faces of the mirror 1 is arranged at an angle slightly staggered from each other in the vertical direction (the direction of mirror axis). Interlacing among these ten portions may be conducted by using the slight angle differences between ten faces of the rotary mirror. The infrared detector converts infrared energy 5 focused by a focusing lens 4 into electric current, amplifies the current by a preamplifier 6, and transmits it via a cable to a processor 7 which processes signals. The reference numeral 8 denotes a silicon window directed toward an object (not shown) and reference numeral 9 denotes a reflector. The camera head sends out two types of synchronous signals to the processor 7. One is PV signal 10 which is given one pulse for one revolution of the mirror 1, and the other is synchronous PH signal 11 given to respective faces of the mirror indicating a blanking period of mirror faces and an unblanking period thereof with thermal image signals of the object. PH signlas are generated in the number of ten pulses for one revolution of the rotary mirror 1. The processor 7 controls writing in the image memory based on those two synchronous signals.
There is also known an infrared video system of digital memory type disclosed in Japanese Patent lay-open No. Sho55-31336 (1980) which stores video signals for one frame in a digital memory, repeatedly reads them out at a high speed, converts them into Japanese Standard Television signals, displays them on a monitor TV screen, and re-writes input video data utilizing blanking periods of TV signals in order to display sequentially new images along with the scanning at the input.
However, although the above mentiond optical-mechanical raster scanning system can detect thermal images in real time as fast as 1/20 sec. for one frame composition, the system cannot always provide precise thermal images if the object moves or the temperature thereof changes during the period of 1/20 sec. As the camera head takes in the images by mechanically scanning infrared images, it has technological limitations in reducing the frame scanning time, thus posing a problem in cost reduction.